The present invention relates to fluoroelastomer seals and compositions therefore, for sealing such fluids as fluorocarbons, chlorocarbons, hydrogen fluoride and hydrogen chloride, and mixtures thereof.
An important use of elastomers is for the production of seals, such as gaskets and O-rings for sealing fluids. Elastomers generally are able to act as a seal because of their resilience and general irapermeability to many fluids. This is important not only to avoid the loss or contamination of valuable materials, but also to protect personal safety, health and the environment.
The requirements for a suitable seal are many. First, of course, it must not degrade or lose its elasticity in contact with the fluids being handled, even at extremes of temperature and pressure. It must not allow these fluids to pass through them easily by permeation. It must not react with these fluids or contaminate them with impurities. And the material must not swell appreciably in contact with the fluids being handled, even at elevated temperatures. For example, if an O-ring in contact with a moving surface swells appreciably, it may be extruded into a close-clearance area where it will be torn by friction. When an O-ring swells while in contact with a fluid under pressure or high temperature, and the pressure or temperature is then reduced, the O-ring may shrink from its extruded position in a way that causes fluid leakage to occur.
Fluoroelastomeric polymers have been utilized extensively for such sealing applications because of their outstanding chemical inertness, solvent resistance and their resistance to high temperatures. In such applications their higher cost than other elastomers is readily justified by their longer life and superior performance.
However, existing fluoroelastomers are not by themselves suitable for sealing certain organic fluorochemical fluids under typical conditions. Because of the chemical similarity of fluorochemical fluids to fluoroelastomers, the fluids tend to dissolve in the fluoroelastomers and thereby cause its swelling and physical deterioration. When such fluorochemicals are manufactured, many of the process streams also contain chlorocarbons and highly corrosive hydrofluoric acid (HF) or hydrochloric acid (HC1), adding to the severity of attack. In particular, 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) is very aggressive in surface attack on seals. HCFC-123 has therefore proven to be one of the most difficult products for which to find a satisfactory seal.
There is a need in the fluorochemical industry for a fluorine-containing elastomeric seal especially suitable for sealing, including containing fluorocarbons, chlorocarbons, hydrogen fluoride, hydrogen chloride and the like, and mixtures thereof.